The US Food and Drug? Administration recently announced new guidelines for recommended levels of salt intake in our diet. These guidelines highlight the fact that certain individuals are at greater risk for the cardiovascular consequences of a high salt intake. The current proposal seeks to define the mechanisms by which risk factors, such as adiposity and environmental stress, contribute to vascular and renal dysfunction associated with the control of sodium balance. The autcicoid, endothelin (ET)-1, functions through ETA and ETB receptors located in a wide range of cell types. Animal studies have revealed an important role for renal tubular ETB receptors in facilitating sodium excretion. Recent studies from the previous funding period have demonstrated that a high fat diet leads to impairment of ETB receptor dependent natriuresis. Therefore, a major goal of the current project is to determine the mechanisms by which adiposity leads to ETB receptor dysfunction to produce alterations in sodium homeostasis, this includes examining a role for angiotensin II and renal sympathetic nerves. In both human and animal models, investigators in the current PPG have observed that acute stress increases plasma ET-1 concentrations. Investigators in Project 1 demonstrated that acute stress in a subpopulation of subjects results in inappropriate Na excretion for a given level of blood pressure. We have also demonstrated that the blood pressure response to acute stress in the Dahl S rat can be attenuated with a combined ETAlB receptor antagonist, but not a selective ETA antagonist. Thus, we propose to explore the degree to which adiposity and genetic factors contribute to ETB receptor function in humans. These issues will be addressed by four aims, two utilizing the Dahl S model that mimics human salt-sensitivity such as frequently occurs in African Americans, and two aims utilizing human subjects. Aim 1 will test the hypothesis that angiotensin II and sympathetic nerve activity mediate ETB receptor dysfunction in a model of adiposity/pre-hypertension, the Dahl S rat on a high fat diet. Aim 2 will test the hypothesis that adiposity results in whole body sodium retention and inflammation that caused by reduced ETB and increased ETA receptor function in the Dahl S rat. Aim 3 will test the hypothesis that the magnitude of the blood pressure response to acute stress in humans is increased as a result of reduced ETB receptor activity. Aim 4 will test the hypothesis that obesity is associated with ETB receptor dysfunction in humans due to actions of angiotensin II.